Antibiotic Resistance Heterogeneity and LasR Diversity within Pseudomonas aeruginosa Populations from Pneumonia in Intensive Care Unit Patients.

We investigate the within-host heterogeneity of 66 P. aeruginosa populations from pneumonia in 51 critically ill ventilated patients, by examining 30 colonies per bronchoalveolar lavage (BAL). We observed differences in antibiotic susceptibility and quorum sensing (QS) phenotypes between the members of 14 (21.2%), and 10 (15.2%) populations, respectively. A significant association was found between QS deficiency and ceftazidime resistance. QS deficiency was associated with various lasR modifications, and observed in 25/51 (49.0%) patients, including 7 who received ≤ 48 hours of ventilation. Our study confirms the need to examine diverse colonies when analysing cultures of bronchoalveolar lavages, particularly in β-lactam-exposed patients, to avoid missing ceftazidime- or imipenem-resistant isolates.